1. Field of the Invention
The present invention relates to a method for producing multifilament superconductive wires of Nb.sub.3 Sn or V.sub.3 Ga filaments having the A15 crystal structure embedded in a Cu or Cu alloy matrix, with the wires containing metal additive elements from the group including Ti, Zr, Hf, V, Nb, Ta, Fe, Co, Ni in the filaments and/or in the matrix, and the superconductive characteristics of the wires are predetermined for medium magnetic fields (below 12 Tesla (H=12T)) as well as for high magnetic fields (12 T and above). The starting materials, with or without cladding, are subjected to one or a plurality of repeated mechanical deformation steps and to a final reaction heat treatment in a temperature range between 500.degree. C. and 1000.degree. C.
2. Technology Review
Superconductive wires that are used to produce high magnetic fields (&gt;12 T) are usually composed of Nb.sub.3 Sn or V.sub.3 Ga filaments embedded in a Cu or Cu alloy matrix. To improve their superconductive properties for high magnetic fields, ternary or quaternary additives have been added to the superconductive intermetallic compounds.
Multifilament superconductive wires based on bronze-Nb.sub.3 Sn with ternary or quaternary additives of, for example, uranium, titanium, zirconium, hafnium, vanadium, tantalum, iron, nickel, palladium, aluminum or others, are disclosed in published European Patent Application No. 48,313. These additives serve to reduce the so-called prestress effect and are alloyed to the niobium and/or copper or to the bronze, respectively. This effect is a result of the different degree of contraction in the Cu-bronze and in the A15 filament during cooling from 1000.degree. K. to 4.2.degree. K. and primarily affects the current carrying capability for high magnetic fields. Primarily, the critical current density J.sub.c is thus reduced considerably compared to the voltage-free state. If the extraneous magnetic field is the same, the reduction is noticeably weakened by the additives.
Tantalum or also titanium and nickel are usually alloyed as additive elements into Nb or V starting material (0.3 to 30 weight % additive element). Since these elements are metals that have a high melting point, the alloys must be produced in an electron beam furnace. Melting processes performed in an electron beam furnace are very complicated and costly. To realize homogeneous distribution of the additive element, repeated remelting in the electron beam furnace is necessary.